If you view drawing from treasures like refinement, and let's say the limit in which you are guaranteed a rare ninja is 70 pulls, I would 10-pull for the first 40 pulls before doing single pulls. IMO, refinements in this game appear to increase in chance with every failure (0/40 has a lower chance of succeeding than a 30/40). Of course, this is just speculation and impossible to prove without a ton of testing or the actual data from Oasis.

As most people draw a rare from 40-60 pulls, I would say the chances are quite high during these pulls. However, I would believe that when you're at 40 pulls and do a 10-pull, it simply takes your chance at 40 pulls and rolls it. If you were to do 10 1-pulls at 40, your chance would increase with every failure, if my theory is correct. Or you can view it as if let's say your 45th pull would get it in both scenarios, a 10-pull would waste 5 extra Seal Scrolls compared to single draws. And again, just my speculation.